A bacterial nanocellulose aerogel, its preparation method and application

Abstract

This invention relates to a bacterial nanocellulose aerogel, its preparation method, and its applications. The preparation method of the bacterial nanocellulose aerogel of this invention includes mixing and reacting bacterial cellulose, hematoxylin oxidase, and a silane coupling agent in deionized water to obtain a self-gel sample; applying ferrous sulfate to the surface of the self-gel sample via point diffusion; and freeze-drying to obtain the bacterial nanocellulose aerogel. This invention uses bacterial cellulose as a precursor to construct a hematoxylin oxidase-iron complex-doped nanocellulose aerogel. The bacterial nanocellulose aerogel of this invention exhibits excellent photothermal properties, with a photothermal conversion efficiency exceeding 85%, and also possesses good mechanical properties, showing broad application prospects in the industrial application of interfacial evaporators.

Description

Technical Field

[0001] This invention relates to the field of interfacial evaporation technology, and in particular to a bacterial nanocellulose aerogel, its preparation method, and its application. Background Technology

[0002] Aerogel is a lightweight solid material formed by the aggregation of nanocolloidal particles, creating a nanoskeleton and nanoporous network structure. It possesses a sponge-like microporous structure, resulting in an extremely large specific surface area and porosity. Furthermore, the pores are filled with a gaseous dispersion medium, exhibiting high porosity, low density, and extremely strong adsorption properties. It is currently one of the lightest solid materials in the world. As traditional seawater desalination becomes increasingly inadequate for providing optimal economic solutions, photothermal conversion materials, as the core of seawater desalination, hold irreplaceable importance due to their superior performance. Therefore, researchers are gradually moving towards biomass and renewable energy sources.

[0003] Seawater desalination refers to the process of separating brine from seawater through various means. Currently, the mainstream seawater desalination technologies used in international commercial applications are divided into two types: thermal and membrane methods. Thermal methods mainly include low-temperature multi-effect evaporation and multi-stage flash evaporation, while membrane methods mainly include reverse osmosis. Photothermal conversion materials are the core component of solar-powered seawater desalination technology, and researchers have conducted extensive studies on them. Commonly used materials include carbon-based materials (carbon nanotubes, graphene, etc.), metal nanoparticles, conjugated polymers, and semiconductor materials. Chinese patent CN116607318A discloses a method for preparing and applying a photothermal conversion material. While it enhances photothermal conversion capabilities and exhibits good antibacterial effects against *Escherichia coli* and *Staphylococcus aureus*, the alkali treatment, redox reactions, and loaded particles in the preparation process significantly increase manufacturing costs and the potential for contamination. Similarly, Chinese patent CN118005489A discloses a method for preparing a photothermal conversion material based on supramolecular eutectic, optimizing the material's economic efficiency and reducing costs. However, its preparation process requires stringent environmental conditions, failing to simultaneously meet the requirements of low carbon emissions, high efficiency, energy conservation, and environmental protection. Furthermore, the mechanical properties of aerogels in existing technologies are poor, making them unsuitable for industrial production. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problems of low evaporation rate and poor mechanical properties of photothermal conversion materials in the prior art.

[0005] To address the aforementioned technical problems, this invention provides a bacterial nanocellulose aerogel, its preparation method, and its applications. The bacterial nanocellulose aerogel of this invention uses bacterial cellulose as a precursor and constructs an oxyhematoxylin-iron complex-doped bacterial nanocellulose aerogel through a point-like diffusion crosslinking process, endowing the aerogel with excellent evaporation properties. Simultaneously, the addition of γ-glycidoxypropyltrimethoxysilane (KH560) improves the mechanical properties of the aerogel, facilitating industrial production. Specifically, KH560 can form a crosslinked structure with bacterial cellulose, enhancing the network stability of the aerogel, thereby improving its compressive strength and toughness. Furthermore, as an organosilane, the flexible segments in the molecule can effectively absorb external stress, improving the material's deformation capacity under impact or tension, effectively reducing the risk of interfacial collapse and brittle fracture, thus improving overall mechanical properties. The crosslinking of oxyhematoxylin forms a dense and uniform crosslinked structure, allowing the aerogel to better disperse and withstand pressure under stress, limiting crack development and propagation, and improving the aerogel's durability. Ferrous sulfate primarily cross-links with hematoxylin and oxychloride. When ferrous sulfate and hematoxylin and oxychloride are mixed, ferrous ions can coordinate with the hydroxyl groups in hematoxylin and oxychloride. In this process, ferrous ions act as cross-linking agents, forming stable composite structures and stable cross-linking networks by coordinating with hydroxyl groups on different molecular chains. The cross-linking structure increases the number of intermolecular connection points, thereby improving the overall structural stability and tensile strength of the material and significantly enhancing its mechanical properties. When these materials are used together, KH560 provides flexibility, while hematoxylin and ferrous sulfate increase strength, and bacterial cellulose increases toughness. Under the combined action of KH560, hematoxylin and oxychloride, the bacterial nanocellulose aerogel of this invention not only has good evaporation performance but also strong mechanical properties.

[0006] The first objective of this invention is to provide a method for preparing bacterial nanocellulose aerogels, comprising the following steps:

[0007] S1. Bacterial cellulose, hematoxylin and silane coupling agent are mixed and reacted in water to obtain a self-gel sample;

[0008] S2. Ferrous sulfate is applied to the surface of the self-gel sample in a dotted diffusion manner, and the bacterial nanocellulose aerogel is obtained after freeze-drying.

[0009] Furthermore, the water used in step S1 is deionized water.

[0010] Furthermore, the silane coupling agent includes γ-glycidoxypropyltrimethoxysilane.

[0011] Further, the amount of hematoxylin added is 10%-100% of the dry weight of bacterial cellulose, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, including but not limited to the values ​​listed above. Preferably, the value is selected from 50%, 60%, 70%, and 80%.

[0012] Furthermore, the amount of γ-glycidoxypropyltrimethoxysilane added is 25%-75% of the dry weight of bacterial cellulose, for example, 25%, 50%, 75%, 100%, including but not limited to the values ​​listed above.

[0013] Further, the amount of ferrous sulfate added is 10%-200% of the dry weight of bacterial cellulose, for example, 10%, 25%, 50%, 60%, 100%, 150%, 200%, including but not limited to the values ​​listed above. Preferably, the values ​​are selected from 50%, 60%, 100%, and 150%.

[0014] Further, the mass ratio of the hematoxylin oxidase to the ferrous sulfate is (1-5):(1-4), for example, 5:1, 2:1, 1:1, 1:2, 1:3, 1:4, including but not limited to the ratios listed above. Preferably, the ratio is selected from 1:1, 1:2, and 1:3.

[0015] Furthermore, the microporous dot permeation device includes a cylindrical body and end caps located at both ends of the cylindrical body. The cylindrical body and the end caps are sealed together, forming a cavity that precisely accommodates the self-gel sample. Several circular through-holes are evenly distributed on the cylindrical body and the end caps; the diameter of each through-hole is 0.430-0.755 mm. Ferrous sulfate is dripped through the through-holes. When the ferrous sulfate reacts with the surface of the self-gel, it diffuses and cross-links outwards from each pore, facilitating the formation of a uniform surface network cross-linking morphology, improving uniformity and aerogel density. During the dot diffusion process from the pores, each pore forms a ring-shaped diffusion area extending outwards and inwards, at which point it intersects with the diffusion rings of other pores. If the pore size is too large, the intersection area will be too large, potentially leading to increased density; conversely, if the pore size is too small, the intersection area will be too small, resulting in blank areas on the aerogel surface, reducing the interfacial reaction area for photothermal conversion, and decreasing efficiency.

[0016] Furthermore, the freeze-drying temperature is -60°C to -40°C, and the freeze-drying time is 24-50 hours.

[0017] Furthermore, after applying ferrous sulfate to the surface of the self-gel sample in a point-diffusion manner, it needs to be left to stand for 20-40 hours to allow it to react fully.

[0018] Furthermore, in step S2, after freeze-drying, a solvent replacement treatment can be performed. Ethanol and tert-butanol are added sequentially to the bacterial cellulose aerogel to remove as many yellow granules as possible precipitated from ferrous sulfate, while simultaneously increasing the surface tension of the bacterial nanocellulose. Tert-butanol has a higher surface tension than ethanol, and during the solvent replacement process, it enhances the hydrophilicity of the prepared aerogel. Moreover, ethanol and tert-butanol are volatile substances and require no further treatment.

[0019] A second objective of this invention is to provide a bacterial nanocellulose aerogel prepared by the above-described preparation method.

[0020] A third objective of this invention is to provide an application of the above-mentioned bacterial nanocellulose aerogel in the preparation of interfacial evaporators.

[0021] The beneficial effects of this invention are:

[0022] 1. This invention uses bacterial cellulose as a precursor to construct a nanocellulose aerogel doped with hematoxylin-iron complex. The hematoxylin and iron ions form a complex, giving the aerogel a black color and improving its light absorption efficiency. Simultaneously, ferrous sulfate is cross-linked via point diffusion, allowing it to diffuse uniformly across the surface of the self-gel sample through a microporous dot permeation device. This point diffusion ensures the uniform diffusion of ferrous sulfate on the sample surface, with each point diffusing outwards and inwards at approximately equal distances. This results in sufficient porosity within the aerogel, enhancing its thermal insulation properties and further improving evaporation efficiency. Therefore, the resulting bacterial nanocellulose aerogel possesses extremely high porosity and extremely low density, which is beneficial for the thermal diffusion of water molecules during interfacial evaporation. Furthermore, the combined effects of bacterial cellulose, hematoxylin, ferrous sulfate, and KH560 result in a dense, three-dimensional structure with cross-linked fibers, further improving the aerogel's mechanical properties.

[0023] 2. The preparation method of this invention has the advantages of simple process flow, green sustainability, high efficiency, and low cost, making it suitable for industrial production. Furthermore, the bacterial nanocellulose aerogel obtained by the preparation method provided by this invention achieves a porosity of over 99% and a density of less than 0.01 g / cm³. 3 This facilitates the thermal diffusion of water molecules during interfacial evaporation. Therefore, the photothermal conversion efficiency of the bacterial nanocellulose aerogel provided by this invention can reach approximately 95% during solar interfacial evaporation. Attached Figure Description

[0024] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0025] Figure 1 This is a process flow diagram of the bacterial nanocellulose aerogel of the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the process of applying the bacterial nanocellulose aerogel of the present invention in the preparation of an interfacial evaporator.

[0027] Figure 3 This is a schematic diagram of the quantitative mold used in this invention;

[0028] Figure 4 This is a schematic diagram of the small-pore mesh permeation device used in this invention;

[0029] Figure 5 This is a process diagram of the present invention for point-like diffusion crosslinking using a small-pore network permeation device;

[0030] Figure 6 The figures are analysis diagrams of the compressive stress-strain curves of Embodiment 1 and Comparative Example 1 of the present invention, wherein A is the compressive stress-strain curve of Comparative Example 1 and B is the compressive stress-strain curve of Embodiment 1.

[0031] Figure 7 XRD patterns for different ferrous sulfate contents;

[0032] Figure 8 These are sample images of Embodiment 1 and Comparative Examples 3-6 of the present invention, wherein a: sample image of Comparative Example 3; b: sample image of Comparative Example 4; c: sample image of Comparative Example 5; d: sample image of Comparative Example 6; e: sample image of Embodiment 1.

[0033] Figure 9 These are SEM images of Embodiment 1 and Comparative Examples 3-6 of the present invention, wherein (a1) and (a2): SEM image of Comparative Example 3; (b1) and (b2): SEM image of Comparative Example 4; (c1) and (c2): SEM image of Comparative Example 5; (d1) and (d2): SEM image of Comparative Example 6; and (e1) and (e2): SEM image of Embodiment 1. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0035] The small-pore mesh permeation device 2 used in this invention is as follows: Figure 4As shown, the microporous dot permeation device 2 includes a cylindrical body 21 and end caps 23 located at both ends of the cylindrical body 21. The cylindrical body 21 and the end caps 23 are sealed together, forming a cavity 20 that can just accommodate the self-gel sample. Several circular through holes 22 are evenly distributed on the cylindrical body 21 and the end caps 23, with a pore diameter of 0.430-0.755 mm. In use, the self-gel sample is placed in the cavity 20, and ferrous sulfate solution is dripped onto the outside of the cylindrical body 21 and the end caps 23. The ferrous sulfate solution is dripped onto the surface of the self-gel sample through the through holes 22, thereby achieving dot-like diffusion cross-linking of ferrous sulfate in the self-gel sample.

[0036] In order to better accommodate the self-gel sample in the accommodating cavity 20 and to allow the ferrous sulfate added from the through hole 22 to better contact the self-gel sample, the present invention also provides a quantitative mold 1, which is adapted to the microporous dot permeation device 2. Therefore, the self-gel sample detached from the quantitative mold 1 can be precisely accommodated in the accommodating cavity 20 of the microporous dot permeation device 2 and fits against the inner wall of the cylinder 21.

[0037] Preferably, the present invention can also have the quantitative mold 1 nested precisely outside the small-pore dot permeation device 2. When the quantitative mold 1 is nested outside the small-pore dot permeation device 2, bacterial cellulose, oxidized hematoxylin, silane coupling agent, and deionized water are directly self-gelled within the small-pore dot permeation device 2. Because the quantitative mold 1 is nested precisely outside the small-pore dot permeation device 2, the self-gelled sample will not leak from the through-holes 22 of the small-pore dot permeation device 2. After self-gelling is complete, the quantitative mold 1 is removed, and then dot-matrix diffusion crosslinking is performed.

[0038] Example 1: Effect of different amounts of ferrous sulfate solution on aerogel

[0039] (1) Take a bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% and mix it with water. Stir magnetically at room temperature for ≥30 min to obtain a bacterial cellulose (BC) aqueous dispersion with a mass fraction of 0.4 wt%.

[0040] (2) Add 50% of the dry weight of bacterial cellulose hematoxylin (OH) and 50% of the dry weight of bacterial cellulose γ-glycidyl etheroxypropyltrimethoxysilane (KH560) and stir evenly for ≥10 min. Then inject it into a 5 mL quantitative mold 1 and let it self-gel for 12 hours.

[0041] (3) Different masses of ferrous sulfate were dissolved in deionized water to prepare ferrous sulfate solutions with different contents. The self-gel samples were placed in the small-pore mesh permeation device 2 and permeated in droplet form to the surface of the self-gel body for point permeation. The gel was allowed to stand for 24 hours to allow the surface reaction to be sufficient. The samples were then frozen in a refrigerator for 24 hours to obtain black solid samples. The mass of ferrous sulfate accounted for 10%, 25%, 50%, 100%, 150%, and 200% of the dry weight of bacterial cellulose, respectively.

[0042] (4) Black solid samples were freeze-dried for 48 hours to obtain bacterial nanocellulose aerogels doped with hematoxylin-iron complex.

[0043] (5) X-ray diffraction was used to characterize the changes in the aggregated structure of the aerogel. Simultaneously, the samples were placed under a xenon arc lamp, and their initial mass was measured. The sample mass was recorded every 5 minutes (for a total of 1 hour) to evaluate the photoevaporation capacity (v1) of each group of samples. The dark evaporation capacity (v2) of each group of samples in the same environment for 1 hour was also recorded to evaluate the evaporation capacity of the bacterial nanocellulose aerogel on simulated seawater. Infrared thermal imaging was used to observe the surface temperature changes of the aerogel. The initial temperature T1 and the stable temperature T2 during the test were recorded. The results are as follows: Figure 7 As shown in Table 1, the analysis results show that, except for the aerogel with 200% ferrous sulfate content, the rest have obvious (101), (101-), (002) and (040) crystal planes, which show the characteristics of type I cellulose. With increasing ferrous sulfate content, the characteristic peaks of cellulose weakened, and new peaks appeared around 19.9°, 24.8°, 27.3°, and 28.6°, attributed to ferrous sulfate and its complexes with hematoxylin and oxyacetylene. After photothermal conversion, the average surface temperature rise of each group of aerogels was around 26.4°C, and the stable temperature T2 remained between 45°C and 47°C. With increasing ferrous sulfate concentration, the η values ​​of each group of aerogel samples were 65.1%, 66.5%, 80.5%, 75.8%, 73.6%, and 71.0%, respectively. Similar to the v1 value, a peak appeared at a ferrous sulfate content of 50%, and the η value could reach over 74% when the ferrous sulfate content was between 50% and 150%. The calculation process for the evaporation rate is shown below:

[0044] Evaporation rate and photothermal conversion efficiency are two key indicators for evaluating the performance of solar water evaporation. Evaporation refers to the amount of water evaporated per unit area per unit time, measured in kg / m³. -2 h -1 The calculation can be performed using formula 1-1:

[0045]

[0046] Where Δm(kg) represents the mass of evaporated water; s(m2 ) represents the evaporation area of ​​the aerogel; Δt(h) represents the evaporation time.

[0047] Photothermal conversion efficiency is an important indicator of a photothermal material's ability to convert light energy into heat energy, and it can be calculated using formula 1-2:

[0048]

[0049] Q = c(T1 - To)(1-4)

[0050] Where m is the evaporation rate under solar radiation minus the evaporation rate under dark conditions, with units of kg / m². 2 h- 1 H LV It is the latent heat required to evaporate water, measured in J kg⁻¹. 1 T1 is the stable temperature of the evaporating surface; T0 is the initial temperature of the evaporating surface; Q is the heat required to raise the water temperature, measured in J kg⁻¹. 1 c is the specific heat capacity of water, with units of 4.2 J g- 1 K- 1 Ein is the energy input of the incident light, measured in kWh / m⁻¹. 2 .

[0051] Under the same conditions, during the evaporation efficiency measurement in the same group of experiments, the porosity of the aerogel reached over 99%. The difference in temperature and humidity will affect the rate of heating and moisture absorption of the aerogel, which may cause some difference between the light evaporation rate and the dark evaporation rate measured at different time periods. However, the final result will not have too much impact, and the result will remain within an error value of about ±3.5%.

[0052] Table 1 Effect of ferrous sulfate addition on aerogel evaporation performance

[0053]

[0054] Example 2: Effect of hematoxylin addition on aerogel evaporation effect

[0055] (1) Take a bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% and mix it with water. Stir magnetically at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%.

[0056] (2) Different masses of hematoxylin oxidase were added, followed by KH560 (50% of the dry weight of bacterial cellulose). The mixtures were stirred evenly for at least 10 minutes each time, and then injected into 5 mL quantitative molds 1 for self-gelling for 12 hours. The amounts of hematoxylin oxidase added were 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% of the dry weight of bacterial cellulose.

[0057] (3) Since it was demonstrated in Implementation 1 that the evaporation rate was optimal when the mass ratio of hematoxylin oxidase to ferrous sulfate was 1:1, ferrous sulfate solution was prepared according to the hematoxylin oxidase content in step (2) with a mass ratio of 1:1. The self-gel samples were then placed in the small-pore mesh permeation device 2 and permeated onto the surface of the self-gel body in droplet form. The gel was allowed to stand for 24 hours to allow the surface reaction to be complete. The sample was then placed in a refrigerator and frozen for 24 hours to obtain a black solid sample.

[0058] (4) Black solid samples were freeze-dried for 48 hours to obtain bacterial nanocellulose aerogels doped with hematoxylin-iron complex.

[0059] (5) The samples were placed under a xenon arc lamp light source, and their initial mass was measured. The sample mass was recorded every 5 minutes (1 hour in total) to evaluate the photoevaporation capacity v1 of each group of samples. The dark evaporation capacity v2 of each group of samples in the same environment for 1 hour was also recorded to evaluate the evaporation capacity of the aerogel on simulated seawater. The surface temperature change of the aerogel was observed using an infrared thermal imager. The initial temperature T1 and the stable temperature T2 during the test were recorded. The results are shown in Table 2. The analysis results show that the η value of each group of aerogels showed a certain trend of first increasing and then decreasing. When the content is low, i.e., when hematoxylin (OH) accounts for 10%-40% of the dry weight of bacterial cellulose (BC), the evaporation efficiency remains at a low level of 70%. However, when the OH content is between 50%-90%, the evaporation efficiency shows a significant trend of first increasing and then decreasing, with the optimal value of 95.4% appearing. That is, when the OH content accounts for 60% of the dry weight of BC, the η value reaches its best of 95.4%. It can also be observed in the table that the η value is higher when the OH content reaches 100%, and it increases again from 71.8% when the OH content is 90% to 76.1%. It is speculated that hematoxylin undergoes a qualitative change at higher contents, thus affecting the final photothermal material performance, but actually increasing its efficiency.

[0060] Table 2. Effects of different amounts of hematoxylin on the evaporation performance of aerogels.

[0061]

[0062] (6) The aerogel prepared by adding 60% of the above-mentioned hematoxylin and oxyacetylene was subjected to solvent replacement treatment. After the aerogel was freeze-dried, ethanol and tert-butanol were added to the bacterial cellulose aerogel in sequence for solvent replacement treatment, and the solvent-replaced bacterial cellulose aerogel was obtained.

[0063] Example 3

[0064] (1) Take a bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% and mix it with water. Stir magnetically at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%.

[0065] (2) First, add hematoxylin oxidase accounting for 60% of the dry weight of bacterial cellulose. Then, add different masses of KH560 and stir evenly for ≥10 min. Then, inject it into a 5 mL quantitative mold 1 and let it self-gel for 12 hours. The amount of KH560 added is 25%, 50%, 75%, and 100% of the dry weight of bacterial cellulose.

[0066] (3) Prepare a ferrous sulfate solution with a content of 60% of the dry weight of bacterial cellulose, place the self-gel sample into the small-pore mesh permeation device 2, and permeate it onto the surface of the self-gel body in the form of droplets. Let the gel stand for 24 hours to allow it to react fully on the surface. Place it in a refrigerator and freeze for 24 hours to obtain a black solid sample.

[0067] (4) Black solid samples were freeze-dried for 48 hours to obtain bacterial nanocellulose aerogels doped with hematoxylin-iron complex.

[0068] (5) The aerogel was placed under a xenon arc lamp light source, and its initial mass was weighed. The sample mass was recorded every 5 minutes (1 hour in total) to evaluate the photoevaporation capacity v1 of each group of samples. The dark evaporation capacity v2 of each group of samples in the same environment for 1 hour was also recorded to evaluate the evaporation capacity of the aerogel on simulated seawater. The surface temperature change of the aerogel was observed using an infrared thermal imager. The initial temperature T1 and the stable temperature T2 during the test were recorded. The results are shown in Table 3. The analysis results show that with the increase of KH560 content, the η value reached 88.3%, 94.1%, 86.5%, and 84.7% respectively, and remained above about 85%. The 50% KH560 content sample group achieved better results. The improvement of mechanical properties can enhance the strength and hardness of the aerogel material, making it more wear-resistant, pressure-resistant, and tensile-resistant, thereby improving its service life and stability. Secondly, it can also increase the impact resistance of the aerogel material, making it less prone to breakage or deformation when subjected to external impact or extrusion. In addition, it can improve the processing performance of the aerogel material, making it easier to perform molding, cutting, and assembly operations. Unlike the sample without KH560, the η value relatively decreased as the KH560 content increased. However, the η value reached its optimal value of 94.1% when the KH560 content accounted for 50% of the dry weight of BC. Therefore, it is speculated that the increase of KH560 may weaken the photothermal conversion ability of the aerogel. However, considering the insufficient strength and water resistance of the aerogel when KH560 is not added or its content is low, and the fact that the evaporation efficiency is weakened when the concentration is too high, the intermediate value of adding 50% KH560 is still preferred.

[0069] Table 3. Effects of different amounts of KH560 added on the evaporation performance of aerogel.

[0070]

[0071] Comparative Example 1

[0072] (1) Take a bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% and mix it with water. Stir magnetically at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%.

[0073] (2) Add 50% of the dry weight of bacterial cellulose hematoxylin and stir evenly for ≥10 min, then inject it into a 5 mL quantitative mold 1 and let it gel for 12 hours.

[0074] (3) Prepare ferrous sulfate with a content of 50% of the dry weight of bacterial cellulose, put the self-gel sample into the small-pore mesh permeation device 2, and permeate it in droplet form to the surface of the self-gel body in a point-like manner. Let the gel stand for 24 hours to allow it to react fully on the surface. Place it in a refrigerator and freeze for 24 hours to obtain a black solid sample.

[0075] (4) Black solid samples were freeze-dried for 48 hours to obtain bacterial nanocellulose aerogels doped with hematoxylin-iron complex.

[0076] (5) Aerogels prepared in Example 1 with ferrous sulfate at 50% of the dry weight of bacterial cellulose were tested. The cyclic compression stress-strain curves of the cylindrical aerogel samples were measured using a universal tensile testing machine equipped with a 500N sensor. Before testing, the sample diameter and height were accurately measured with vernier calipers. The compression and recovery rates were set to 5 mm / min, and the maximum compressive strain was 80%. Finally, the compression modulus and elastic recovery rate were calculated based on the test results. The mechanical property results are shown in […]. Figure 6 (A is the compressive stress-strain curve of Comparative Example 1, and B is the compressive stress-strain curve of Example 1). Figure 6 Analysis shows that with the addition of KH560, the elastic recovery rate of the sample increased from 39.68% to 53.39%, indicating that KH560 has a certain cross-linking and reinforcing effect on the aerogel material itself. In other words, KH560 improves the mechanical properties of the material without affecting its hydrophilicity. These data conclude that the addition of KH560 promotes the enhancement of the strength of the three-dimensional aerogel structure.

[0077] Comparative Example 2

[0078] (1) Take a bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% and mix it with water. Stir magnetically at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%.

[0079] (2) Add 50% of the dry weight of bacterial cellulose hematoxylin and stir evenly for ≥10 min, then inject it into a 5 mL quantitative mold 1 and let it gel for 12 hours.

[0080] (3) Prepare ferrous sulfate with a content of 50% of the dry weight of bacterial cellulose, put the self-gelling sample into device 2, and pour the prepared ferrous sulfate solution into device 2 so that the self-gelling sample is immersed in the ferrous sulfate solution; freeze in a refrigerator for 24 hours to obtain a black solid sample.

[0081] (4) The black solid sample was freeze-dried for 48 hours to obtain black nanocellulose aerogel doped with hematoxylin-iron complex.

[0082] (5) Aerogels prepared in Example 1 with ferrous sulfate mass equal to 50% of the dry weight of bacterial cellulose were selected for testing. Samples from Example 1 and Comparative Example 2 were placed under a xenon arc lamp. While weighing their initial mass, the sample mass was recorded every 5 minutes (for a total of 1 hour) to evaluate the photoevaporation capacity (v1) of each group of samples. The dark evaporation capacity (v2) of each group of samples in the same environment for 1 hour was also recorded to evaluate the evaporation capacity of the black aerogel on simulated seawater. The surface temperature change of the aerogel was observed using an infrared thermal imager, and the initial temperature T1 and stable temperature T2 during the test were recorded. The results are shown in Table 4. In the same environment, the aerogel formed by point diffusion achieved a high efficiency of 97.5% in the photothermal conversion process. Compared with the sample formed by the impregnation method in Comparative Example 2, the efficiency was increased by 11.7%, effectively improving the photoevaporation efficiency. Through surface-diffuse cross-linking, ferric sulfate can diffuse more uniformly on the surface of the self-gel. While diffusing outwards, it also diffuses inwards at approximately equal distances. Due to its own weight, it diffuses inwards at a certain gradient from bottom to top, creating sufficient internal voids to provide effective heat retention and improve the thermal stability temperature of the photoreaction rate, thereby increasing evaporation efficiency. The resulting bacterial nanocellulose aerogel achieves extremely high porosity and extremely low density, which is beneficial for the thermal diffusion of water molecules during interfacial evaporation. The resulting bacterial nanocellulose aerogel maintains good mechanical properties while exhibiting high photothermal conversion efficiency. The preparation method of bacterial nanocellulose aerogel provided by this invention is green and sustainable, highly efficient, and low-cost, making it suitable for industrial production.

[0083] Table 4. Effect of crosslinking method on aerogel evaporation performance

[0084]

[0085] Comparative Example 3

[0086] A bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% was mixed with water and magnetically stirred at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%. This dispersion was then injected into a 5 mL quantitative mold 1 and allowed to self-gel for 12 hours. The sample was then frozen for 24 hours to obtain a solid sample. The solid sample was freeze-dried for 48 hours to obtain bacterial nanocellulose aerogel.

[0087] Comparative Example 4

[0088] A bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% was mixed with water and magnetically stirred at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%. KH560, accounting for 50% of the bacterial cellulose dry matter, was added and stirred evenly for ≥10 min. The mixture was then injected into a 5 mL quantitative mold 1 and allowed to self-gel for 12 hours. The sample was then frozen for 24 h to obtain a solid sample. The solid sample was freeze-dried for 48 hours to obtain bacterial nanocellulose aerogel.

[0089] Comparative Example 5

[0090] A bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% was mixed with water and magnetically stirred at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%. Oxidized hematoxylin and oxyacetylene (60% of the dry weight of bacterial cellulose) was added and stirred evenly for ≥10 min. The mixture was then injected into a 5 mL quantitative mold 1 and allowed to self-gel for 12 hours. The sample was then frozen for 24 h to obtain a solid sample. The solid sample was freeze-dried for 48 hours to obtain bacterial nanocellulose aerogel.

[0091] Comparative Example 6

[0092] A bacterial cellulose aqueous dispersion with a mass fraction of 0.8 wt% was mixed with water and magnetically stirred at room temperature for ≥30 min to obtain a bacterial cellulose aqueous dispersion with a mass fraction of 0.4 wt%. A ferrous sulfate solution containing 60% of the bacterial cellulose dry weight was prepared. The self-gel sample was placed in a small-pore mesh permeation device 2 to allow for droplet-like permeation onto the surface of the self-gel, and the gel was allowed to stand for 24 hours to allow for sufficient surface reaction. The sample was then frozen for 24 hours to obtain a solid sample. The solid sample was freeze-dried for 48 hours to obtain nanocellulose aerogel.

[0093] The aerogel prepared in Example 1, with ferrous sulfate at 50% of the dry weight of bacterial cellulose, was used for testing. Digital photographs of Comparative Examples 3-6 and Example 1 were taken from the same angle, as shown below. Figure 8 The surface morphology of the aerogel was characterized using scanning electron microscopy, and the results are shown in the figure below. Figure 9The analysis results show that (a) the PBC aerogel is white. Since KH560 is a colorless and transparent substance, the color of BC-560 aerogel in (b) remains unchanged after its addition, but its three-dimensional framework is improved, making its appearance more three-dimensional and improving the local collapse phenomenon. Hematoxylin is yellowish-brown, so after its addition to PBC, the color of (c) did not change significantly. Similar to the addition of KH560, its mechanical properties increased, and its surface collapse was improved, which may be due to cross-linking that occurred during the addition process. Ferrous sulfate (FE) is green but is easily oxidized to ferric iron and turns yellow. Therefore, in (d), the BC-FE aerogel is clearly yellow after oxidation, but its surface shows obvious pitted textures and pores. The size difference is obvious, and it is speculated that the content has a significant impact on the appearance of the aerogel. In (e), the BC-OH-FE-560 aerogel prepared by the optimal process formula is black. Through the comparison of samples, it can be inferred that the main reason is that the complex obtained by the chemical reaction between hematoxylin and iron ions affects the color of the final product. BC-OH-FE-560 has a relatively flat appearance, but the density is increased. As shown in SEM image (a2), at low magnification, the aerogel prepared by PBC shows obvious lamellar cavity structure. This large cavity is caused by the growth of large ice crystals during freezing. With the addition of KH560, as shown in Figure (b2), its surface smoothness is improved, and the structure develops from two-dimensional layered structure to three-dimensional structure, making its structure more three-dimensional. Figures (a1) and (b1) show the microstructure of the aerogel cavity wall at high magnification. In PBC, bacterial cellulose fibers interweave and stack to form a relatively dense lamellar structure. With the addition of KH560, the "sharpness" of the aerogel cavity wall edge is reduced, the boundaries between fibers gradually become blurred, and the cavity wall edge gradually becomes thicker. Figures (c1) and (c2) show that, compared with PBC, with the addition of hematoxylin oxidase, the lamellar cavity of the original sample microstructure becomes larger, the boundaries between fibers are clear, the three-dimensional cavity structure is obvious, the cavity wall at high magnification has a bending tendency, and nodes appear on its surface. Figures (d1) and (d2) clearly show the "bundled" texture on its surface. It is speculated that the appearance of this morphology is related to the formation of self-gel by ferrous sulfate impregnation, and the texture is formed by the bundles. The addition of ferrous sulfate blurs the boundaries between fibers, which increases the smoothness of its surface.In the optimal sample image at high magnification shown in (e1), obvious cross-linking nodes can be observed. However, the connection of fibers can also be clearly observed outside the nodes. The dense cross-linking of fibers is presumably due to the increased structural strength and dense three-dimensionality. At low magnification, the cavity is more three-dimensional. Compared with PBC, the distance between the layered structures has increased. Therefore, it is presumed that the pore volume of the aerogel has increased within a certain range. This also increases the amount of still air contained in the aerogel, thereby increasing its thermal insulation performance. In the process of contact with liquid, the photothermal conversion of bacterial nanocellulose aerogel can better maintain the continuous rise of water temperature under the interfacial evaporation mode and effectively improve the photothermal conversion efficiency.

[0094] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing bacterial nanocellulose aerogel, characterized in that, Includes the following steps: S1. Bacterial cellulose, hematoxylin oxidase, and silane coupling agent are mixed and reacted in water to obtain a self-gel sample, wherein the amount of hematoxylin oxidase added is 10%-100% of the dry weight of bacterial cellulose. S2. Ferrous sulfate is applied to the surface of the self-gel sample in a point-diffusion manner, and the bacterial nanocellulose aerogel is obtained after freeze-drying. The dotted diffusion method is achieved through a small-pore mesh penetration device; The small-pore network permeation device includes a cylinder and end caps located at both ends of the cylinder. The cylinder and the end caps are sealed together. The cylinder and the end caps together form a cavity that can just accommodate the self-gel sample. Several circular through holes are evenly distributed on the cylinder and the end caps. The diameter of the through hole is 0.430-0.755 mm.

2. The preparation method according to claim 1, characterized in that, The silane coupling agent includes γ-glycidoxypropyltrimethoxysilane.

3. The preparation method according to claim 1, characterized in that, According to the preparation method of claim 1, the silane coupling agent is added at an amount of 25%-75% of the dry weight of bacterial cellulose.

4. The preparation method according to claim 1, characterized in that, The amount of ferrous sulfate added is 10%-200% of the dry weight of bacterial cellulose.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the hematoxylin oxidase to the ferrous sulfate is (1-5):(1-4).

6. The preparation method according to claim 1, characterized in that, The freeze-drying temperature is -60°C to -40°C, and the freeze-drying time is 24-50 hours.

7. A bacterial nanocellulose aerogel prepared by the preparation method according to any one of claims 1-6.

8. The application of the bacterial nanocellulose aerogel according to claim 7 in the preparation of interfacial evaporators.

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